1. Field of the Invention
The present invention relates to a vibration-type angular velocity sensing device used for navigation systems, attitude controls and the like for motorcars.
2. Description of the Related Art
Conventionally, an angular velocity sensing system using a mechanical rotor-based gyroscope has long been used as an inertial navigation system for an aircraft and a ship.
The mechanical rotor-based gyroscope is excellent in stability and performance but, on the other hand, it has disadvantages owing to its large size, high cost, and short life.
In recent years, in place of the mechanical rotor-based gyroscope, development of a vibration-type gyroscope using a vibration-type angular velocity sensing device for practical use has been proceeding.
The angular velocity sensing device comprises a long fine vibration body formed of a metallic material having constant elasticity such as elinvar, a piezoelectric element to drive the vibration body by applying AC voltage, and another piezoelectric element to detect the vibration which is in proportion to the angular velocity created by a Coriolis force induced by the rotational movement.
For instance, a vibration-type gyroscope using a vibration-type angular velocity sensing device is proposed in JP 6-241815 A. The outline thereof will be explained briefly with reference to FIG. 15 and FIG. 16.
The angular velocity sensing device shown in FIG. 15 and FIG. 16 is prepared as follows. Metallic material such as elinvar is shaped into a long regular triangular pillar to be served as a vibration body 91. Piezoelectric elements 92, 93 for driving and detecting respectively, and a piezoelectric element 94 for feedback are adhered at a middle point on each surface along the longitudinal direction of the regular triangular pillar. Supporting members 95 and 96 are welded onto nodes of vibration of the vibration body 91, and the whole angular velocity sensing device is held by fixing the supporting members 95 and 96 onto a base portion 97, as shown in FIG. 16.
In the angular velocity sensing device, the vibration body 91 is vibrated at its resonant frequency in the y-axis direction shown in FIG. 15 by applying AC voltage having the same frequency as the resonance frequency of the vibration body 91 to the piezoelectric elements 92 and 93 for driving and detecting of the vibration body, and to the piezoelectric element 94 for feedback thereof.
At this time, if the vibration body 91 receives a rotational angular velocity .omega. having a rotational axis in the z-axis direction, namely, in the direction of the length, a Coriolis force is induced in the x-axis direction, and the piezoelectric elements 92 and 93 develop voltages which are the same in magnitude but opposite in polarity.
By respectively applying the output voltages of the two piezoelectric elements 92 and 93 to two input terminals of a differential amplifier which is not shown in these figures, and then, eliminating the superposed AC voltage to leave the generated voltage alone, and furthermore, by performing synchronous detection using the resonance frequency, a detection signal in accordance with the magnitude of the angular velocity can be obtained.
However, such a conventional vibration-type angular velocity sensing device is said to have the following disadvantages.
First, since the whole angular velocity sensing device is held in a manner that the nodes of vibration of the vibration body in a triangular-pillar shape are welded to the supporting member at two points on the ridgeline portion, the shock-resistance characteristic thereof is low.
Second, since the supporting member needs to be welded accurately on the positions where the nodes of vibration of the vibration body are created, it requires considerably difficult work and many assembling processes. Accordingly, the price becomes expensive.
Third, since the axis of rotation of which angular speed is to be detected, takes in the direction of the length of the vibration body, the height in size of the whole angular velocity detecting element is determined by the length of the vibration body. Accordingly, reduction of the size is limited.